Photopatternable Electrolytes for Conducting Polymer Actuators
Abstract: Electroactive polymers (EAPs) are materials that can change their dimensions or shape in response to electric stimulation. They have attracted considerable interests for their applications as soft, lightweight and silently operating polymer actuators. One significant group of EAPs is conducting polymers. Conducting polymer actuators are driven by the volume variations of the conducting polymers, which is a result of the ion diffusion into/out of the conducting polymer matrix during an electrochemical redox process in the presence of an electrolyte. Over other actuation mechanisms, conducting polymers have many attractive features such as being electrically controlled, low activation voltage of 1V or less, large generated strain and high stress, and good biocompatibility. To miniaturize or fabricate microarrays of these electrochemical actuators that can operate in open air, micropatterns and microstructures of polymer gel electrolyte are desired. In this thesis, we develop photopatternable polymer gel electrolytes based on different routes of polymerization network formation and present their application in conducting polymer (micro)actuators.First, photopatternable electrolyte patterns were developed through free radical photopolymerization of methacrylate monomers as conductive photoresist by a conventional photolithographic process. By immobilizing those electrolyte micropatterns on top of the electroactive polypyrrole layer, solid-state microactuator was achieved although with reduced movement as compared to microactuators operating in liquid electrolytes. The result shows a reliable and scalable microfabrication method for soft, on-chip polymer based microactuators operating in air using standard photolithography to broaden the microfabrication toolbox. It also shows the possibility to batch fabricate complex microsystems such as microrobotics and micromanipulators based on these solid state on-chip microactuators.Second, a thiol acrylate mixed mode photopolymerization was used to prepare a novel soft and flexible ionogel with a reactive surface and a high ionic conductivity. The developed ionogel materials are well suited to be used with conventional photolithography as a negative-toned ionically conducting photoresist. Lithographic capabilities of the material enable direct fabrication of ionic conductive micropatterns and 3D microstructures using conventional photolithography. It has also been successfully utilized in a high-resolution soft imprint lithography process to pattern the surface of the ionogel film. This new type of ionogel has been demonstrated in the application of micro electrochromic micropatterns and twisting actuators. A Double Diaphragm Active Polymer Actuator (DDAPA) was also constructed using this novel ionogel to demonstrate its application as a microinjection tool, a flow regulator, and as a fully disposable unidirectional hybrid pump for active microfluidic components.Finally, a novel platform to develop micropatternable ionogels with tunable mechanical and surface properties was established using the Michael addition reaction. Polymerization kinetic studies showed that the ionic liquid not only acts as an ion source but also a co-catalyst in the polymerization. Ionogels with tailorable surface and mechanical properties were prepared using three approaches: offstoichiometry, methacrylate addition, and dithiol chain extender addition. 3-dimensional ion conducting structures were constructed by bonding the flexible ionogel film together using the ionogel solution as an ionic adhesive. In addition, micro-patterns of the ionogels were obtained by photolithography and soft imprinting lithography. To illustrate the potential of the reactive surfaces, two 3-dimensional devices were created from a flat structure: a tube actuator with two embedded actuator pairs and a box with a flexible electrode forming a taxel. These interesting results demonstrate that thiol acrylate Michael chemistry provides a platform to prepare various forms (films, micro-patterns, 3-dimensional structures, and adhesive) of ionogels for the next generation of flexible electrochemical devices.
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